Thambidurai and Park have proposed an algorithm for Interactive Consistency that retains
resilience to the arbitrary (or Byzantine) fault mode, while tolerating more faults of simpler
kinds than standard Byzantine-resilent algorithms. Unfortunately, and despite a published
proof of correctness, their algorithm is flawed. We detected this while undertaking a formal
verification of the algorithm.

We present a corrected algorithm that has been subjected to mechanically-checked formal
verification. Because informal proofs seem unreliable in this domain, and the consequences
of failure could be catastrophic, we believe formal verification should become standard for
algorithms intended for safety-critical applications.